1. Field of the Invention
The present invention relates to a passenger conveyor such as an escalator or a moving pathway.
2. Description of the Prior Art
The passenger conveyors have been popularized as essential transportation service equipments in buildings. Recently, the use of the passenger conveyors has been extended to outdoor crowded areas, such as underground stations of subway, stations of elevated railroad and the like, to provide a part of city transportation network.
The passenger conveyors for such extended uses are required to operate under severe environmental conditions, as compared with passenger conveyors in conventional uses such as escalators of department stores. For instance, the passenger conveyors for such extended uses have to meet with various requirements particularly in respect of durability, such as corrosion-resistant property high enough to withstand the corrosive action of underground water, surface hardness sufficiently high to avoid damages caused by the contact of passengers. Thus, there is an increasing demand for passenger conveyors which fully meet with these requirements.
Typical passenger conveyor of the prior art is constituted by movable elements such as a plurality of steps connected in series in an endless manner to carry passengers thereon, handrails adapted to run in synchronization with the steps and so on, and stationary elements such as balustrade panels constituting balustrades, handrail frames, outer decks, inner decks disposed behind the balustrade panels and in opposite relationship to the outer decks, and so on.
The balustrades are each composed of a plurality of handrail frame sections connected smoothly and continuously in the longitudinal direction of the conveyor, such as substantially semicircular handrail frame sections, curvilinear handrail sections connected to the semicircular sections, and an inclined handrail section.
The handrail frames constituting the balustrades and the treadboards of the steps were conventionally made of extruded structural materials of an aluminum alloy. Thus, the conventional conveyors had shortcomings in respect of the durability and corrosion-resistant surface property.
More specifically, a literature "Corrosion-Resistant Alloys" issued in 1962 by Japan Metal Engineering Association contains an article concerning alkali-resistant properties of metals as shown in the table below:
______________________________________ kinds of metal corrosion rate (mg/dm.sup.2 /day) ______________________________________ aluminum 25,000 stainless steel 1 iron 1 ______________________________________ (5% caustic soda solution used)
It will be seen from above table that aluminum is corroded at a rate which is 25,000 times of those of stainless steel and iron. This raises quite a serious problem because concrete, which exhibits a high alkalinity, is usually laid in those areas where the passenger conveyors are installed and hence the bad influence of the alkalinity on the aluminum is unavoidable. This is also shown by the fact that most of already-constructed passenger conveyors installed in such areas have been corroded more or less. On the other hand, aluminum exhibits a hardness as low as 13 in Shore hardness scale and, therefore, is liable to be damaged by passenger's shoes and the like.
As a solution for these problems, it is conceivable to make handrail frames and treadboards from stainless steel which exhibits a hardness and corrosion resistance which are 2 times and 2500 times of those of aluminum, respectively.
It is to be pointed out, however, that stainless steel has been recognized as a material having extremely poor workability and formability in machining and plastic working, respectively, and for this reason, is not in use in any commercial scale.